The existence of any infectious agent in a highly acidic human stomach is contentious, but the chance finding of Helicobacter pylori is by no means an accident. Once H. pylori colonises the gastric mucosa, it can persist for a lifetime, and it is intriguing why our immune system is able to tolerate its existence. Some conditions favour the persistence of H. pylori in the stomach, but other conditions oppose the colonisation of this bacterium. Populations with high and extremely low prevalence of H. pylori provide useful insights on the clinical outcomes that are associated with this type of infection. Adverse clinical outcomes including peptic ulcer disease and gastric cancer depend on a delicate balance between a harmless inflammation and a more severe kind of inflammation. Is the only good H. pylori really a dead H. pylori? The jury is still out.